Automatic speed control of motors



Oct. 4, 1949. G. w. SWITZER 2,483,678

AUTOMATIC SPEED CONTROL OF MOTORS Filed April 6, 1946 E Pg i? m 9 Q m S! g INVENTOIIC.

George W. Sw/fzer BY Siz m I Aff'y Patented Oct. 4, 1949 UNITED STATE PATENT OFFICE AUTOMATIC SPEED CONTROL OF MOTORS AppllcationAprll 0. 1946, Serial No. 660,090

1 Claim. 1

This invention relates to an apparatus to regulate the speed of a motor drive so as to control the speed of the motor, irrespective of fluctuation of line voltage.

The principal object of this invention is to produce a device which may be attached to any standard motor circuit without altering its construction.

A further object is to provide means for instantaneously detecting any line voltage change.

the same the figure is a schematic wiring diagram of one use to which my invention can be placed.

There are many places where it is desirable to have a feed arrangement which will automatically compensate for different working conditions and for line-voltage changes, as for instance, the feed of the arc lamp as used in motion picture projectors, or the feed of the electrodes of an automatic welding machine.

In motion picture projection machines it is necessary that the carbons be fed toward each other at such a rate that a predetermined gap between the abutting ends is maintained. This gap cannot vary more than one two-hundredths of an inch without aflecting the screen illumination. I

It has heretofore been necessary for the operator to watch the arc and to manually adjust the feed in order to compensate for voltage changes or changes in the characteristic of the carbons being consumed.

I have therefore perfected an apparatus which may be connected to any motor-feed mechanism in order to speed up or retard the motor and thereby compensate for any change in the line voltage.

The single view represents a diagrammatic wire diagram of the present invention.

In accomplishing my object I employ the usual 0 motor 5, which is connected to one side of the line by wires 6 and ill, to the contact I of switch 8. The other side of the motor is connected through a variable resistance 9 and wires l I and I2 to contact l3 of switch 8.

We will now assume that the motor I is to control the feed of an arc lamp, having a positive carbon and a negative carbon, which have to be fed toward each other as they are consumed by means of a shaft So on which is carried a friction wheel 5b engaging the carbon A to move the same toward and from the carbon B as shown in general in the patent to Kennedy, #2,145,010, and at such a speed thatthe gap between the adjacent ends of the carbons will not vary more than two one-hundredths of an inch from a predetermined setting, irrespective of the hardness or softness of the carbons, or of hard or soft spots in the carbons, which will affect the rate of consumption of the carbons.

The wire II is connected to the carbon "A," which is the negative carbon, and the positive carbon "13 is connected to the positive wire III.

In order to detect and control the speed of the motor 5 I employ one or more electronic tubes and in the present showing I have used two tubes and a relay, which tubes and relay are connected to the circuit above described, as follows: The positive wire [0 is connected to a variable resistance I4, the opposite end of which is connected by a wire [6 to the armature ll, of the relay iii.

The positive wire i0 is' also connected by wire l9 to one side of the relay l8 and also through a resistance 2| to the plate of the tube 23. The opposite side of the relay I8 is connected by wire 24 to the plate 26 of the tube 21.

Inserted in the wire 24 is a milliammeter 28.

The variable contact of the resistance I4 is connected to the grid 29 of the tube 23 and also to one end of a resistor 3|, the opposite end of which thus places a negative bias on the cathode of thetube 21 as the'cathode 44 is connected to the filament-lead 4i.

The contact 46 of the relay I8 is connected by wire 41 to the motor 5. At 48 I have shown a resistance and lamp 49 connected in series between the wires l9 and 41, which lamp will indicate when the apparatus is in operation.

Assuming that the above has been connected to a motor circuit and, for a matter of discussion, to the motor circuit of an arc lamp feed;

also, that the line voltage is varying, the follow-.

ing will then occur:

If the voltage rises, the grid 29 will become more positive than it is at the present time, through the efiect of the resistor 3|, and at normal voltage no current will be flowing from the cathode 32 to the plate 22; but, as soon as the grid becomes positive, current can flow, thus causing the grid 34 of the tube 21 to become more positive, causing current to pass from cathode N to plate 26 and relay l8 to attract its armature l1, completing a circuit from wire IE to wire 41 and shorting out resistor 9. This will speed up the motor to move the carbons A and B toward each other until the positive voltage on the grid 29 is lowered, at which time the negative bias will act to stop the flow of current through the tube 23. This, in turn, will stop the flow of current in the tube 21 and relay l8 will open, causing the motor to slow down as the resistance 9 is again placed in the motor feed circuit.

The relay, therefore, acts to cut in and out the resistance 9 at a rate controlled by the action of the tubes controlled by voltage changes in the line. Inasmuch as the tubes are very sensitive to voltage variations the control of the motor is practically instantaneous for such an installation.

It will also be apparent that in welding, voltage changes take place due to poor contact variations in the resistance of the parts being welded, etc., and therefore this invention would control equally as well the speed of the driving motor of a welding machine.

It is to be understood that the form of my invention herewith shown and described is to be taken as a preferred example of the same and that various changes relative to the material, size, shape and arrangement of parts may be resorted to without departing from the spirit of the invention or the scope of the subjoined claim.

Having thus described my invention, I claim:

The combination in voltage controlling means, of a motor, a current supply having negative and positive sides, a current consuming apparatus having an adjustable element, a conductive connection between one side of said supply and one terminal of said apparatus, a mechanical connection between said motor and said apparatus for adjustment of the latter, a resistance connected to one terminal of said motor, a conductive connection between said side oi the current supply and the resistance, a conductive connection extending from the second side 01' said current supply and connected to the remaining termini of the apparatus and motor in multiple, a normally open relay having a fixed contact and a movable contact, a conductive connection between one of said contacts and the motor and having connection with the motor between the first mentioned motor terminal and said resistance, a conductive connection between the last mentioned terminus of said apparatus and the remaining relay contact, said relay including a magnet operable when energized to close said contacts, a conductive connection between the second side of the current supply and one terminus of the magnet, a tetrode, a. conductive connection between the plate of said tetrode and the remaining terminus of said magnet, a second tetrode, a conductive connection between the grid of the firsttetrode and the cathode of the second tetrode, a conductive connection including a resistance and connecting the plate of the second tetrode with the connection to the first mentioned terminal of the magnet, and a conductive connection including a resistance and connecting the grid of the second tetrode to the first mentioned resistance.

GEORGE W. SWITZER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,662,434 Palmer Mar. 13, 1928 1,942,587 Whitman Jan. 9, 934 1,944,756 Quarles Jan. 23, 1934 2,028,572 Strong Jan. 21, 1936 2,145,010 Kennedy et a1. Jan. 24, 1939 2,175,009 Anderson Oct. 3, 1939 2,265,687 Chapman Dec. 9, 1941 2,391,086 Crandell Dec. 18, 1945 

